1. Field of the Invention
The present invention relates to a liquid crystalline polyester resin for extrusion molding having high heat resistance and an excellent extrusion molding property.
2. Description of the Related Art
Liquid crystalline polyester resins (hereinafter, sometimes referred to as liquid crystalline polymer) have the features that their heat resistance is high, their flowability in molten state is excellent and the like, and therefore, are used in wide variety of fields mainly including the electronic material field as injection molding materials which can be precisely molded. They are called collectively as liquid crystalline polymers, however, generally classified into type I, type II and type III based on level of heat resistance thereof (e.g., "Liquid Polymer for Molding Design", Sigma Shuppan (1995)). Of them, those called type I are composed of specific wholly aromatic components, and are materials having especially high heat resistance, that is, a deflection temperature under load of 250.degree. C. or more, among liquid crystalline polymers.
In addition to excellent heat resistance of liquid crystalline polymers, applications to extrusion molding fields such as films, vessels and the like have been intensively studied by utilizing features such as an excellent gas barrier property, low dielectric property, chemical resistance and the like.
However, it is generally said that liquid crystalline polymers are materials not suitable for extrusion molding field since their melt viscosity is low, and therefore, the anisotropy thereof is high and the like.
Therefore, a lot of investigations have been made. For example, Japanese Patent Application Laid-Open (JP-A) No. 2-3430 discloses film-formation of an aromatic polymer comprising (1) oxybenzoic acid and (2) 2,6-naphthoic acid as repeating units. JP-A No. 5-186614 discloses the film-formation of semi-aromatic materials prepared by adding components such as ethylene glycol and the like in addition to the above-described oxybenzoic acid and 2,6-naphthoic acid. Also, combination with other resins has been studied for the purpose of improving the extrusion molding property thereof. For example, JP-A No. 61-78862 discloses a composition composed of a liquid crystalline polymer and polyethylene terephthalate, and JP-A No. 63-270760 discloses film-formation of a composition composed of a liquid crystalline polyester and an aromatic polycarbonate. However, in any of them, liquid crystalline polymers are of type II and type III, heat resistance is low, or, a material having low heat resistance is combined for improvement of processability in a liquid crystalline polymer comprising a type I liquid crystalline polymer. Therefore, in the present conditions, sufficient heat resistance originally owned by a type I liquid crystalline polymer has not been obtained yet.